1Off-line scan procedure - When the device is idle for some period of time, it may start various self-diagnostic procedures, including just wandering into the surface to read sectors here and there. You may observe this by letting your system idle (provided that no background process requests disk access) and listening to the hard drive. It will soon start to operate "on its own" - this is an off-line scan underway. This is done to detect any possible growing defects before they become critical.